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Transmission electron microscopy specimens typically exhibit local distortion at thin foil edges, which can influence the absorption of X-rays for quantitative energy dispersive X-ray spectroscopy (EDS). Here, we report a numerical, three-dimensional approach to model the geometry of general specimens and its influence on quantification when using single and multiple detector configurations. As a function of specimen tilt, we show that the model correctly predicts the asymmetric nature of X-ray counts and ratios. When using a single detector, we show that complex specimen geometries can introduce significant uncertainty in EDS quantification. Further, we show that this uncertainty can be largely negated by collection with multiple detectors placed symmetrically about the sample such as the FEI Super-X configuration. Based on guidance provided by the model, we propose methods to reduce quantification error introduced by the sample shape. The source code is available at https://github.com/subangstrom/superAngle.

Here we report the influence of key experimental parameters on atomically resolved energy dispersive X-ray spectroscopy (EDX). In particular, we examine the role of the probe forming convergence semi-angle, sample thickness, lattice spacing, and dwell/collection time. We show that an optimum specimen-dependent probe forming convergence angle exists to maximize the signal-to-noise ratio of the atomically resolved signal in EDX mapping. Furthermore, we highlight that it can be important to select an appropriate dwell time to efficiently process the X-ray signal. These practical considerations provide insight for experimental parameters in atomic resolution energy dispersive X-ray analysis.

Quantitative agreement on an absolute scale is demonstrated between experiment and simulation for two-dimensional, atomic-resolution elemental mapping via energy dispersive X-ray spectroscopy. This requires all experimental parameters to be carefully characterized. The agreement is good, but some discrepancies remain. The most likely contributing factors are identified and discussed. Previous predictions that increasing the probe forming aperture helps to suppress the channelling enhancement in the average signal are confirmed experimentally. It is emphasized that simple column-by-column analysis requires a choice of sample thickness that compromises between being thick enough to yield a good signal-to-noise ratio while being thin enough that the overwhelming majority of the EDX signal derives from the column on which the probe is placed, despite strong electron scattering effects.

Here we report a numerical approach to model a four quadrant energy dispersive X-ray spectrometer in the transmission electron microscope. The model includes detector geometries, specimen position and absorption, shadowing by the holder, and filtering by the Be carrier. We show that this comprehensive model accurately predicts absolute counts and intensity ratios as a function of specimen tilt and position. We directly compare the model to experimental results acquired with a FEI Super-X EDS four quadrant detector. The contribution from each detector to the sum is investigated. The program and source code can be downloaded from https://github.com/subangstrom/superAngle.

A phase diagram-assisted powder processing approach is shown to produce low-oxygen (0.06 wt%O) ZrB2 ceramics using minimal B4C additions (0.25 wt%) and spark plasma sintering. Scanning electron microscopy and scanning transmission electron microscopy with elemental spectroscopy are used to identify “trash collector” oxides. These “trash collector” oxides are composed of manufacturer metal powder impurities that form discreet oxide particles due to the absence of standard Zr–B oxides found in high oxygen samples. A preliminary Zr–B–C–O quaternary thermodynamic database developed as a part of this work was used to calculate the ZrO2–B4C pseudobinary phase diagram and ZrB2–ZrO2–B4C pseudoternary phase diagrams. We use the calculated equilibrium phase diagrams to characterize the oxide impurities and show the direct reaction path that allows for the formation of ZrB2 with an oxygen content of 0.06 wt%, fine grains (3.3 μm) and superior mechanical properties (flexural strength of 660 MPa).

Summary Here, we present a sample preparation approach that simplifies the thinning of very brittle wide bandgap semiconducting materials in cross-section geometry for (scanning) transmission electron microscopy. Using AlN thin films grown on sapphire and AlN substrates as case studies, we demonstrate that high-quality samples can be routinely prepared while greatly reducing the preparation time and consumables cost. The approach removes the sample preparation barrier to studying a wide variety of materials by electron microscopy.

In recent years, X-ray signal collection efficiency in energy dispersive X-ray spectrometry (EDS) has been significantly improved by incorporating state-of-the-art four-quadrant Super-X detectors in aberration-corrected microscopes [1, 2] and has enabled routine atomic-resolution EDS elemental mapping, as shown in Figure 1a. The breakthrough in detector technology has sparked interest in quantifying the chemical information directly from atomically resolved EDS maps [3-5]. In order to obtain an atomic-resolution EDS map, the specimen however must be tilted to a low index zone axis, resulting in different orientation with respect to each detector. This will inevitably result in different Xray signals arriving at each detector due to their different absorption distances and effective take-off angles. Such a variation could largely affect the ability to accurately quantify the overall EDS spectrum from four Super-X detectors without precautions as evidenced in this work. Therefore, understanding the X-ray signal variation from each detector under tilted specimen condition becomes both experimentally and theoretically important as a starting point for atomic-resolution EDS quantification.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.